Nested fields not fetched by storeMixin

When using the nested-field attribute, the targeted resource is not fetched by the store. For example, with this:

<sib-display
  bind-user
  nested-field="inbox"
></sib-display>

We only take the inbox field we find in the http://[host]/[current-user] resource.

The problem is that the inbox field can be incomplete, depending of the depth of the server.

Instead, we need to fetch the URL of the resource http://[host]/[current-user]/[inbox-id]